The present invention generally relates to torque sensors, and in particular to a method and device for non-contact torqueshaft magnetic field measurement under harsh environmental conditions.
Torque measurement may be required for output control or for changing supplied power in applications where power is transmitted via a rotating drive shaft. Prior art methods have included the process of applying strain gauges to the surface of the drive shaft to measure torque. More recently, research and development efforts continue to produce various non-contact methods using magnetoresistive sensors.
It is known in the present state of the art that shaft torque can be measured by emplacing magnetoelastic regions on the shaft and detecting magnetic field changes via a magnetic sensor. For example, U.S. Pat. No. 4,896,544, discloses a magnetoelastic torque transducer for providing an electrical signal indicative of torque applied to a shaft. The transducer includes a primary coil installed in a cylindrically-shaped yoke. Operation of the transducer, however, requires that a varying current be supplied to the coil to produce a varying magnetic field.
Many conventional systems utilize sensing coils to detect changes in the magnetic field. For example, U.S. Pat. No. 4,989,460 discloses a magnetorestriction-type torque sensor employing a plurality of detector coils disposed in an axial arrangement along a rotary body. Such coil configurations suffer from the shortcomings that detector coils do not generally provide consistently repeatable measurements, detector coils tend to be bulky, and alignment of such coil-type sensors is generally difficult. Moreover, the present state of the art does not disclose magnetic sensors suitable for use in harsh environments, such as elevated temperatures.
As can be seen, there is a need for a method and device for obtaining reliable torque measurements from rotating members operating in harsh environments.